Process for manufacturing an article with a polychrome picture imposed on the surface thereof

ABSTRACT

A polychrome image is produced on the surface of an article by depositing on a solid dielectric layer a thin film of a unilaterally conducting metal or alloy thereof to a thickness of at least 500 A followed by breaking the film into separate areas in conformity with the shape of the picture to be reproduced, the areas being electrically insulated from one another. Thereafter the areas are subjected to selective anodic oxidation at a constant current density of less than 10 ma./cm.2 and at working voltages which vary from one area to another in a range of 5 to 250 volts.

United States Patent [54] PROCESS FOR MANUFACTURING AN ARTICLE WITH A POLYCHROME PICTURE IMPOSED ON THE SURFACE THEREOF 3 Claims, 4 Drawing Figs.

[52] U.S.Cl 204/35 N, 204/18, 204/56 [51] lnt.Cl C23b 9/00 [50] Field of Search 204/18, 32,

[5 6] References Cited Primary Examiner-John H. Mack Assistant Examiner-W. 1. Solomon Attorney-Waters, Roditi, Schwartz & Nissen ABSTRACT: A polychrome image is produced on the surface of an article by depositing on a solid dielectric layer a thin film of a unilaterally conducting metal or alloy thereof to a thickness of at least 500 A followed by breaking the film into separate areas in conformity with the shape of the picture to be reproduced, the areas being electrically insulated from one another. Thereafter the areas are subjected to selective anodic oxidation at a constant current density of less than 10 ma./cm. and at working voltages which vary from one area to another in a range of5 to 250 volts.

PAIENTEDNHV 9 YI 3. 6 1 9. 3 8 5 sum 2 or 2 PROCESS FOR MANUFACTURING AN ARTICLE WITH A POLYCIIROME PICTURE-IMPOSED ON THE SURFACE THEREOF This invention relates to the field of decorative and protective surface finishing and, more particularly, to methods of producing a polychrome picture on the surface of an article.

The invention may find extensive application in diverse industrial fields, such as machine building, optics, watchand clock-making, and jewelry etc.

The production of polychrome film coatings that resist mechanical and weather effects is a challenging problem and involves numerous difficulties.

It is an object of the present invention to provide articles having a polychrome surface with sharply defined color boundaries and to provide a process for producing the same, that will render it possible to reproduce accurately the desired picture, be it a drawing or a portrait or miniature, in a wide color range and with sharply defined color boundaries and, if necessary, with half-tones, and that will also be instrumental in obtaining coatings noted for their good mechanical strength, adherence, and resistance to moisture, acid or alkaline media, as well as to sharp temperature fluctuations and to radiation.

These and other objects are accomplished by the provision of an article with a polychrome picture imposed on the surface thereof, wherein on a solid dielectric layer coated with an at least 500 A. thick film ofa unilaterally conducting metal or of alloy thereof there is produced a transparent anodic oxide film whose thickness varies from 100 to 6,000 A. at different areas of the article, thereby imparting different coloration to different areas of the picture due to light interference phenomena.

In the present context, the term unilaterally conducting metal denotes a transition metal whose oxide film exhibits low asymmetric electron conduction,

The article surface may be bright or dull, or have a combination of bright and dull areas, depending upon the brilliance (degree of fineness) of the dielectric layer surface.

Where the degree of fineness of the dielectric surface layer is in the ll to 14 range, the article in question will have a bright surface, whereas a dull surface will be obtained if the degree offineness equals 7 to 10.

The process of manufacturing an article having a polychrome picture imposed on its surface consists in depositing on a solid dielectric layer (substrate) a thin film of a unilaterally conducting metal or of an alloy thereof, the film thickness being at least 500 A. The thus obtained film is further broken into separate areas which conform to the shape of the picture to be reproduced, provision being made to insulate electrically each film area, followed by subjecting said areas to selective anodizing in type I or II electrolytes at a constant current density of not greater than 10 ma./cm. the working voltage being in the 5 to 250 range, depending upon the film area to be anodized.

It is expedient to effect the electric insulation of said film areas from one another by the provision of contour clearances.

The unilaterally conducting metal may be selected from the group consisting of tantalum, niobium, and titanium.

Where a titanium film is subjected to anodic oxidation in a 0.0IM solution of ammonium tartrate, the process should be carried out at a constant current density of 0.5-2.0 ma./cm. the desired coloration of selected film areas being attained with the following voltages applied:

Presented hereinbelow is a detailed description of the method, according to the invention, for the manufacture of articles having polychrome pictures imposed on the surface thereof, illustrated by the accompanying drawings. wherein:

FIG. 1 is a plan view which shows a dielectric substrate with the film of a unilaterally conducting metal deposited thereonto;

FIG. 2 is a similar view except that the film of a unilaterally conducting metal is broken by contour clearances which insulate each film area in conformity with the picture to be reproduced;

FIG. 3 shows the treatment of the article in an electrolytic cell, the article being seen in plan to show the varicolored film areas thereof; and

F104 is a cross-sectional view taken along line AA in FIG. 3 of an anodic film of variable thickness which serves for the coloration of specific film areas due to interference phenomena.

The method of manufacturing an article having a polychrome picture imposed on the surface thereof involves three consecutive stages:

1. Depositing a thin film F of unilaterally conducting metal at least 500 A. thick, on the surface ofa solid dielectric substrate 8 (FIG. 1).

When the article to be processed is made of a material which is devoid of dielectric properties, the surface of the article in question should be preliminarily coated with an insulating dielectric layer applied by any known technique, such as vacuum deposition, cataphoresis, or anodic oxidation.

2. Dividing the thus obtained film of unilaterally conducting metal or of an alloy thereof into separate areas in conformity with the nature of the picture to be reproduced, this operation being accomplished by the provision of contour clearances that bring about electric insulation of separate film areas F from one another (FIG. 2).

3. Subjecting separate areas of the film to selective anodic oxidation for obtaining an oxide film of varying thickness which makes possible the coloration of each area into the desired color (FIGS. 3 and 4).

The first stage, i.e., the deposition of the film of a unilaterally conducting metal or of an alloy thereof, such as tantalum or titanium, onto the solid dielectric substrate can be effected by any known technique, e.g., by cathode sputtering or by the pyrolysis of an organometallic compound.

The second stage of the process involves tracing the picture on the film of a unilaterally conducting metal or of an alloy thereof by the provision of contour clearances, which clearances insulate electrically separate areas of the film one from another, the application of said clearances being feasible by a variety of techniques, such as mechanical milling by means of a copying device, chemical milling of contour clearances which consists in screening the film areas with a protective varnish applied through the agency of a templet. followed by etching the unscreened clearances. and photolithography.

The photolithographic technique consists in coating the-film of a unilaterally conducting metal with a light sensitive emulsion layer, followed by the application of the contour clearance pattern by contact printing, and thereafter developing the light sensitive emulsion so that the clearances to be etched become exposed, subjecting the intact emulsion to heat treatment for imparting chemical stability thereto, and, finally, carrying out the chemical etching of the contour clearances.

The third stage of the present process consists in selective anodic oxidation of separate areas of the film of unilaterally conducting metal, wherein anodic polarization is effected in type I or type II electrolytes, provision being made for contacting each separate film area by means of a contact that leaves on the article being processed no traces discernible to the naked eye. The cathode is made from a self-passivating or noble metal that is conductive to uniform oxidation.

The type I or II electrolytes are selected from 0.1M to 0.00lM solutions of organic or mineral acids and salts in highpurity water (demineralized water having a resistivity of 0.5 Mohm or higher). The pH of the solutions used is maintained in the 4 to 7 range, the electrolyte temperature being maintained below 150 C., preferably 2030 C. The anodizing process is conducted at a constant current density (imA/cm const) of not greater than 10 mA/cm preferably at a current.

density in the 0.1 to 1 ma./cm. range, provided the voltage increases spontaneously in the 5 to 250 V range, the voltage applied to different film areas being different so as to provide for the formation of oxide fi 1ms having the desired thickness. Hence, the thickness of an oxide film on each area is controlled by the application of an appropriate voltage. Voltage selection is effected either visually or by means of calibration tables which correlate the voltage applied and the color obtained for each unilaterally conducting metal-electrolyte combination. Anodic oxidation results in the formation of a transparent oxide film of dissimilar thickness at different film areas, so that light interference phenomena produce polychromaticity of the surface of the finished article.

Presented below is a calibration table which correlates the voltage applied and color produced for tantalum, niobium, and titanium films subjected to anodic oxidation at a current density of 0.1 to 2 ma./cm. in a 0.01M solution of ammonium tartrate acidified to a pH of 4-5.5.

Voltage V Color 5 to 27 brown 18 to 36 blue 24 to 45 light blue 40 to 80 yellow 76 to 100 red 110 to 155 green 85 to 180 red-purple 160 to 250 crimson red It is to be noted that intermediate shades of the aboveidentified colors are obtainable at intermediate values of voltages applied as compared to those indicated for pure colors.

In order to obtain superior-quality films it is expedient to continue the anodizing process at a constant voltage (V=const.), this technique being conductive to elimination of oxide film faults. This treatment results in a sharp increase of the ohmic resistance of the film and in a concomittant improvement of its corrosion-resisting properties. The anodizing time is governed by the desired corrosion resistance of the resultant film, so that where the requirements are moderate, a process time of 5 minutes is adequate. If, however, stringent requirements are imposed on protective characteristics of the coating in question, the anodizing time at V=const. should be several scores of minutes, the mean anodizing period being 30-40 minutes.

The anodic oxidation process may be accomplished in a still bath or in a fluent electrolyte cell, the latter technique being preferable, inasmuch as electrolyte circulation makes possible the filtration ofthe electrolyte.

Upon termination of the anodic oxidation process, the finished article is washed with high-purity water and dried at a temperature of 120-150 C. for at least 1 hour. Where recourse is had to the fluent electrolyte cell, it is expedient to wash the finished articles in the cell in question.

The surface of the finished articles may be bright, dull or a combination of both, these characteristics being dependent upon the brilliance of the dielectric material surfaces. In case the dielectric layer surface exhibits a degree of fineness equal to 1 1-14, the finished article would be bright, whereas for a degree of fineness in the 7-10 range, the article would be dull.

The present invention makes it possible to obtain an anodic coating noted for its good adherence to the metal film, as well as for high mechanical strength under normal service conditions and at sharp temperature fluctuations in the 50 to +150 C. range, and also for its resistance to radiation. The present coating exhibits corrosion-resisting properties under tropical conditions. It is practically insoluble in organic or mineral acids or mixtures thereof, irrespective of concentration or proportions, except for hydrofluoric acid and salts thereof.

The manufacture of articles, according to the present invention, inv olve s the consumption of an insignificant amount of the unilaterally conductin g rnetal. W V

The present method is conducive to large-scale production of the articles, according to the invention.

The fields of application of the present method are diverse and include the manufacture of souvenirs, badges, and jewelry (pendants, earrings, bracelets, etc.); finishing of instrument parts, insignia, emblems, and topographic layouts; production of largeand small-size panels, with or without a picture imposed thereon, for interior and exterior decorations of public buildings, etc., and also for making stained-glass panels.

The present invention is illustrated hereinbelow by the description of an exemplary embodiment thereof with reference to the manufacture of an article having a polychrome picture imposed on its surface.

EXAMPLE.

An ordinary glass plate having a degree of surface fineness equal to 14 is degreased and dried at 300 C., and thereafter preliminary evacuation 1-5 X10" mm. Hg working vacuum obtained by introducing nrgon into the system discharge voltage current l-Z X10" mm. Hg 3.2-3.5 kV

Next, use is made of the photolithographic technique to transpose the picture to be reproduced on the thus obtained tantalum film. To do so, the metal film is degreased and thereonto is applied a 0.5 ucm. thick light sensitive emulsion based on naphthoquinonediazide.

The light sensitive emulsion is applied by means of a sprayer, the layer thus obtained is dried in a dust-free chamber at a temperature of 7080 C. and thereafter maintained at said temperature for 15 minutes.

The plate coated with the light sensitive layer is next placed under a photographic templet of the picture to be reproduced and exposed to ultraviolet light (wave length, 2,000 to 3,000 A.) for a period of 30 seconds, the photographic templet being made so that only the contour clearances are irradiated, while the surface of separate areas remains unexposed. (Pertinent data on the manufacture of the templet and preparation of the light sensitive emulsion are described below).

The emulsion applied to the irradiated areas, e.g., contour clearances, undergoes decomposition and can be readily removed by dipping the plate for 20-30 sec. into a 10 percent solution of trisodium phosphate. Next, the plate is washed with high-purity water until a neutral reaction is attained, dried at a temperature of 70-80 C. for 15 minutes and thereafter subjected to heat treatment at a temperature of C. for a period of5 min. in order to enhance the acid-resisting properties of the emulsion layer. Then, the plate is cooled and subjected to chemical milling (etching) along the contour clearances with an etchant consistingof mixture of concentrated hydrofluoric and nitric acids in a ratio of 1:10 by volume. Etching is accomplished by submerging the plate into the etchant for a period of 20 to 30 seconds, followed by washing the plate with high-purity water.

The protective layer is removed from the unexposed areas of the tantalum film by an acetone-dioxane mixture (1:1 by volume). Now, the plate surface consists of separate areas that are electrically insulated from one another, the arrangement of said areas conforming to the image to be reproduced, as

shown at F -F in FIG. 2. The plate treated in the manner disclosed hereinabove can next be subjected to anodizing.

The anodic oxidation of areas I, 2, and 3 of the tantalum film (FIG. 3) is conducted in an electrolytic cell 4 furnished with tantalum cathode 5. The electrolyte consists of 0.01M solution of ammonium tartrate maintained at a pH of 6. Current supply to separate film areas is effected by means of tantalum rods 6, 7, and 8 bent at right angles and sharpened at the contact end. Current rating is 1.00 ma./cm. the voltage applied being selected in compliance with the color-voltage correlation table for the tantalum film-electrolyte (ammonium tartrate) system:

Areal, blue color V=36V; l =l0 ma; 1- =6 min.;1,=20 min. cm.

Area 2, yellow color; V=73V; I =8 ma.; 1" =12 min.; -r" =l4 min.

Area 3, red color V=94V; l =12 ma.; f -=16 min.; 'r" =l() min.

ranodizing time at i=const.;

r"anodizing time at V=const.

The anodic oxidation having been terminated, the plate is extracted from the cell, washed with high-purity water and dried at a temperature of 100 C.

The light sensitive emulsion employed is prepared in a dark room (red light) by mixing 7.2 grams of novolak dissolved in 50 ml. of dioxane with 4.6 grams of naphthoquinonediazosulfonate also dissolved in 50 ml. of dioxane.

The photographic templet is manufactured as follows. The picture to be reproduced is drawn to 10:1 scale on paper. The picture in question consists of three fields of dissimilar area separated from one another by contour clearances 0.5 mm. wide. The three separate areas are inked, and the contour clearances remain uninked. The picture is photographed on a plate to yield a sharp positive print.

Depending upon the light sensitive emulsion used, which might be either positive or negative, the photographic templet should be also positive or negative, respectively.

In the present embodiment of the invention, use is made of the positive emulsion.

The finished article is colored blue, yellow and red. In view of the fact that the degree of fineness of the dielectric surface equals l4,the article will be bright.

We claim:

1. A process of manufacturing an article with a polychrome image imposed on the surface of said article, which method comprises depositing on a nonconductive solid dielectric substrate a thin film of a unilaterally conducting metal or of an alloy thereof, the thickness of said film being at least 500 A., followed by dividing said film into separate areas in conformity with the shape of the picture to be reproduced by masking and etching said film, insulating said areas electrically one from another and thereafter varying the film thickness of the areas by subjecting said areas to selective anodic oxidation in type I or II electrolytes at a constant current density of less than l0 ma./cm. and at working voltages which vary from one area to another in a range of 5 to 250 V to effect colors of the polychrome image.

2. A process according to claim 1, wherein the electric insulation of said areas from one another is effected by providing contour clearances therebetween.

3. A process according to claim 1, wherein said film is tantalum and anodic oxidation is conducted at a current density of 0.5 to 2 ma./cm. in a 0.0lM solution of ammonium tartrate, the following voltages being applied to obtain the colors specified hereinbelow:

brown 22 to 27 V blue 33 to 36 V light blue 40 to 45 V yellow 65 to 73 V red 93 to 98 V green ll5lol50 V. 

2. A process according to claim 1, wherein the electric insulation of said areas from one another is effected by providing contour clearances therebetween.
 3. A process according to claim 1, wherein said film is tantalum and anodic oxidation is conducted at a current density of 0.5 to 2 ma./cm.2 in a 0.01M solution of ammonium tartrate, the following voltages being applied to obtain the colors specified hereinbelow: brown 22 to 27 V blue 33 to 36 V light blue 40 to 45 V yellow 65 to 73 V red 93 to 98 V green 115 to 150 V. 